Characterization of Theileria equi genotypes in horses in Israel, the Palestinian Authority and Jordan

Equine theileriosis caused by Theileria equi is endemic in the Middle East, where it causes a severe disease as well as widespread subclinical infection. The aim of this study was to evaluate the diversity of T. equi genotypes in Israel and the neighboring Palestinian Authority and Jordan. Blood samples from 355 horses from Israel, the Palestinian Authority and Jordan were tested for the prevalence of T. equi DNA. Two hundred and fourteen (60%) were found positive for T. equi infection by PCR. Of those, the 18S rRNA (1458 bp) and the EMA-1 (745 bp) genes of T. equi were sequenced from 15 horse samples that represent Israel's geographical distribution together with four samples from the Palestinian Authority and two from Jordan. The results were used for genotype characterization and phylogenetic analysis of T. equi in the equine population in Israel and its surroundings. Three 18S rRNA genotype clades were found in Israel (A, C and D) with clade D being the most prevalent and included all four isolates from the PA. In contrast, the EMA-1 gene showed little diversity with all sequences clustering in the same clade apart from one Jordanian sequence. Results suggest that although the Israeli horse population is small and relatively confined geographically, it is probable that the genetic variability, which was found among Israeli horses, is a result of introduction of horses from other countries. It also suggests that the EMA-1 gene is probably not a good target for the evaluation of variance in T. equi populations. Characterization of the different genotypes prevalent in a certain region is important in order to map out the intra-species sequence heterogeneity of the parasite, which is needed in order to develop new diagnostic tools and vaccines.